1. Field of the Invention
The present invention relates to an image forming apparatus for a copying machine, a printer, a facsimile or the like.
2. Related Background Art
Recently, an electrophotographic system composite machine equipped with all of output terminals such as a copying machine, a printer and a facsimile is extensively spreading as an output terminal compatible with a network. As one of serious problems of such an electrophotographic system composite machine, a duty cycle of an apparatus body is taken up. This duty cycle can be defined as the limited number of formed images during which the apparatus body can be normally operated without the maintenance of a serviceperson, and this limited number depends largely on a life of a photosensitive drum.
Furthermore, from the viewpoint of ecology, it is a serious theme to eliminate wastes, that is, to reduce expendables, to extend the lives of the expendables, and to improve the reliability of the expendables.
Additionally, in the apparatus body, digitalization makes progress from a conventional analog device, and it is also an additional theme to make the cost of a digitalized apparatus body equal to or less than that of the analog device.
Moreover, as for the copying machines and the printers, black-and-white machines have heretofore mainly been used, but full-color machines are rapidly increasing in offices and the like. In addition to the machine bodies themselves, it is also requested that the running cost of the full-color machines is substantially equal to that of the black-and-white copying machines. To attain this object, a technology capable of drastically reducing Total Cost Ownership (TCO) is desired.
Under such circumstances, in recent years, there has extensively spread a color image forming apparatus (e.g., a four-throw tandem type color image forming apparatus) comprising a plurality of electronically photosensitive bodies (photosensitive bodies) as image bearing bodies and a transferring belt (a recording material bearing body) for bearing and transferring a recording material. In this kind of color image forming apparatus, transferable toner images of different colors formed on the respective photosensitive bodies (hereinafter referred to simply as xe2x80x9cthe toner imagexe2x80x9d) are transferred in turn onto the recording material borne on the transferring belt to obtain a color image.
In the image forming apparatus in which there is repeated a process of transferring the toner image formed on the surface of the photosensitive body onto the recording material (mainly a paper), it is essential every process to sufficiently remove the toner (the residual toner) remaining on the surface of the photosensitive body which has not been transferred onto the recording material in a transfer step.
Therefore, as cleaning means, a number of suggestions have heretofore been made, but the cleaning means for scraping away the remaining toner by a cleaning blade comprising an elastic material such as a urethane rubber is of a simple and compact constitution and is low in cost. Besides, such cleaning means has an advantage of an excellent toner removing function and the like, and is therefore put to practical use extensively. As a rubber material of the cleaning blade, there is generally used a urethane rubber having a high hardness and rich elasticity, excellent friction resistance, mechanical strength, oil resistance, and ozone resistance.
In the aforesaid image forming apparatus, however, the following first to fourth problems have occurred.
As the first problem, a frictional force between the photosensitive body and a residual material thereon caused by the cleaning blade is inconveniently increased with time. This fact has been confirmed by an experiment. Owing to a filming film formed with time, adhesion and affinity between the cleaning blade and the surface of the photosensitive body and between the residue and the surface of the photosensitive body increase, so that frictional force increases. In addition, it has been found that the frictional force depends with time on the shape of the photosensitive body surface formed by initial grinding.
An increase in the frictional force is considered to be due to an increase in shearing stress of the cleaning blade, shearing stress between the toners and shearing stress in the vicinity of the photosensitive body surface. As a result, the increase in the frictional force is considered to lead to the occurrence of chipping (localized chipping of an edge) of the cleaning blade, the fusion of the toner due to heat generated by an increase in permanent strain shearing force, and the occurrence of fatigue wear due to an increase in internal stress of the photosensitive body. Incidentally, the excessive reduction in the frictional force reduces the adhesion between an edge section of the cleaning blade and the surface of the photosensitive body, so that a frictional effect intrinsic in the blade on the surface of the photosensitive body is lost. That is, when a continuous image formation is performed in a system in which the frictional force is excessively low, the filming film is easily formed, so that there is a possibility that the frictional force conversely increases, as described above.
As the second problem, the composite machine is used not only as the copying machine but also as the printer in recent years as described above, so that the number of formed images in one operation is increased and hence the residual material easily adheres to the surface of the photosensitive body. Applications for a feeder function and a sorter function are also fulfilled, so that as one job (the number of the formed images), a continuous operation of 4000 sheets or more has become possible. For example, in the case of an A4 size machine of 50 sheets/minute, a continuous image forming operation for 80 minutes or more is to be performed as understood by simple calculation. Under such circumstances, it is considered that ambient temperature in the vicinity of the transferring belt reaches about 50xc2x0 C., and an abutting portion (a nip portion) between the cleaning blade and the surface of the photosensitive body reaches a temperature more than the above temperature. As a result, the residual material is often stuck or coagulated on the surface of the photosensitive body.
Regarding the third problem, as the grain size of the toner becomes smaller, it is possible to perform developing with an excellent dot reproducibility and resolution, and sharpness and image quality of the toner image are improved, but in this case, too, since the specific surface area increases, sticking force per unit weight of the toner to the photosensitive body surface is increased, and the cleaning performance of the photosensitive body surface is deteriorated. As the grain size of the toner becomes smaller, since fluidity of the toner is deteriorated, greater amount of additive becomes necessary, and as a result, there arises a problem in which wear or chipping of the cleaning blade, a localized linear scratch, and the like occur on the photosensitive body surface as described above.
As the fourth problem, in recent years, a polymer toner is being diversified to improve transferring efficiency, eliminate and the like the coating of mould releasing agent on fixing means. However, a toner manufactured by the polymerization method generally has a high sphericity. When the sphericity is improved, and a counter blade system generally used in the past is adopted, passage of the toner increases if abutment pressure as usual is used, and it becomes necessary to increase the abutment pressure further. As a result, a localized shear force is applied to the cleaning blade, causing chipping of the edge.
In order to prevent nonconformities of the first through fourth problems as described above, a method has been used in the past in which a lubricant is coated in advance on the edge section of the cleaning blade to reduce the frictional force between the photosensitive body and the cleaning blade.
For example, when spherical grains are used as the lubricant, since the lubricating performance of the grain itself is extremely high, its effect as the lubricant is excellent, however, since the lubricant has a property to easily pass through the edge section of the cleaning blade, the lubricant fell from the edge section due to fine vibrations of said edge section, and thus the lubricating effect was lost. As a measure to cope with the situation, an attempt and the like to increase the coating amount of the spherical grains was made, but a problem resulted in which the peeling amount of the lubricant also increased corresponding to an increase in the coating amount of the spherical grains, and the peeled lubricant existed on the photosensitive body preventing the exposure, and caused a defect in the image.
In addition, if unshaped grains are to be used as the lubricant, passing of the lubricant through the edge section of the cleaning blade can be reduced, but the grains itself lack in lubricating capacity, and so-called chattering (abnormal vibration) is likely to occur between the photosensitive body surface and the cleaning blade during initial stage until a foreign matter, the toner and the like accumulates in the vicinity of the edge section and sufficient lubrication effect is obtained.
As described above, by working a device for a lubricant coating method, stable conditions of the cleaning blade can be obtained to a certain extent, but it was difficult to obtain a stabilized performance over a long period of time.
On the other hand, as another prior art aiming at stabilization of cleaning, Japanese Patent Application Laid-Open No. 4-335387 and Japanese Patent Application Laid-Open No. 11-218953 are disclosed.
In Japanese Patent Application Laid-Open No. 4-335387, a constitution is descried in which a fluorine compound or silicone compound is caused to be contained in a cleaning blade of a urethane rubber so as to maintain a dynamic friction coefficient between an image bearing body and the cleaning blade in a range of 0.2 to 1.2.
Further, in Japanese Patent Application Laid-Open No. 11-218953, a constitution is described in which fluororesin grains are caused to be contained in the outermost layer of a photosensitive body to improve the cleaning performance of a spherical toner and maintain the coefficient of friction between the photosensitive body surface and the urethane blade to be less than 1.0.
However, in either constitution of the above, since the available range of the coefficient of friction is about 1.0, it is difficult to adjust the coefficient of friction within this range, and a high cost and unstable cleaning performance are caused to occur easily.
The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus in which the damage of a cleaning blade and the occurrence of defective cleaning can be prevented when a substantially spherical toner is swept away, to obtain a stable cleaning performance.
In order to achieve the aforesaid object, the present invention comprises an image forming apparatus comprising a first image bearing body for bearing an image formed with a substantially spherical toner,
transferring means for transferring a toner image on said first image bearing body onto a second image bearing body,
a cleaning member, abutting on said first image bearing body, for sweeping away the toner remaining on said first image bearing body after a transferring operation by said transferring means, wherein
it is simultaneously satisfied that said first image bearing body contains a fluororesin on its surface,
a content ratio F (% by weight) of said fluororesin is in a range of 10xe2x89xa6Fxe2x89xa650,
a surface roughness Rz (xcexcm) of said first image bearing body is Rz less than 5.0,
and a dynamic friction coefficient xcexc between said first image bearing body and said cleaning member is in a range of 0.5xe2x89xa6xcexcxe2x89xa62.5.
These and other objects and advantages of the invention may be readily ascertained by referring to the following description and accompanying drawings.